Method and apparatus for transmitting and receiving downlink control information in a mobile communication system supporting uplink packet data service

ABSTRACT

A method and apparatus for transmitting and receiving downlink control information in a mobile communication system supporting an uplink packet data service are provided. To transmit packet data in an HARQ mobile communication system, a second transceiver receives an RG as rate control information from a first transceiver. The second transceiver sets the allowed maximum data rate of an HARQ process to which the RG is applied to the allowed maximum data rate of an HARQ process previous to the HARQ process, if the RG indicates hold. The second transceiver transmits packet data within the set allowed maximum data rate to the first transceiver.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.11/272,823, filed Nov. 15, 2005, now issued as U.S. Pat. No. 8,045,513,which claims priority under 35 U.S.C. §119(a) to an application entitled“Method And Apparatus For Transmitting And Receiving Downlink ControlInformation In A Mobile Communication System Supporting Uplink PacketData Service” filed in the Korean Intellectual Property Office on Nov.15, 2004 and assigned Serial No. 2004-93283 and to an applicationentitled “Method And Apparatus For Transmitting And Receiving DownlinkControl Information In A Mobile Communication System Supporting UplinkPacket Data Service” filed in the Korean Intellectual Property Office onNov. 16, 2004 and assigned Serial No. 2004-93743, the contents of bothof which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a cellular Code DivisionMultiple Access (CDMA) communication system. More particularly, thepresent invention relates to a method and apparatus for transmitting andreceiving downlink control information in the case where an EnhancedUplink Dedicated transport CHannel (E-DCH) is used.

2. Description of the Related Art

A 3^(rd) generation mobile communication system using WCDMA based on theEuropean Global System for Mobile communications (GSM) system andGeneral Packet Radio Services (GPRS), Universal Mobile TelecommunicationService (UMTS) provides mobile subscribers or computer users with auniform service of transmitting packet-based text, digitized voice, andvideo and multimedia data at or above 2 Mbps irrespective of theirlocations around the world.

In particular, the UMTS system uses a transport channel called the E-DCHin order to further improve the packet transmission performance ofuplink communications from a User Equipment (UE) to a Node B(interchangeable with a base station). For more stable high-speed datatransmission, Adaptive Modulation and Coding (AMC), Hybrid AutomaticRepeat reQuest (HARQ), Node B-controlled scheduling, and shorterTransmission Time Interval (TTI) were introduced for the E-DCHtransmission.

AMC is a technique of determining a Modulation and Coding Scheme (MCS)adaptively according to the channel status between the Node B and theUE. Many MCS levels can be defined according to available modulationschemes and coding schemes. The adaptive selection of an MCS levelaccording to the channel status increases resource use efficiency.

HARQ is a packet retransmission scheme for retransmitting a packet tocorrect errors in an initially transmitted packet. HARQ is branched intoChase Combining (CC) and Incremental Redundancy (IR). The HARQ schemeadopts N-channel Stop and Wait (SAW) to increase data rate. In theN-channel SAW HARQ, a transmitter transmits different data in first toN^(th) Transmission Time Intervals (TTIs), and determines whether toretransmit the data or transmit new data in (N+1)^(th) to 2N^(th) TTIsaccording to Acknowledgement/Non-Acknowledgement (ACK/NACK) received forthe transmitted data. N TTIs are processed by separate HARQ processesand each of HARQ processes for the (N+1)^(th) to 2N^(th) TTIs is calledan i^(th) HARQ process. N is an integer greater than 0 and the HARQprocess number i is an integer number ranging from 1 to N.

Node B-controlled scheduling is a scheme in which the Node B determineswhether to permit E-DCH transmission for the UE and if it does, anallowed maximum data rate and transmits the determined data rateinformation as a scheduling grant to the UE, and the UE determines anavailable E-DCH data rate based on the scheduling grant.

Shorter TTI is a technique for reducing retransmission time delay andthus increasing system throughput by allowing the use of a shorter TTIthan the shortest TTI of 10 ms provided by 3GPP Rel5.

FIG. 1 illustrates uplink packet transmission on the E-DCH in a typicalwireless communication system.

Referring to FIG. 1, reference numeral 100 denotes a Node B supportingthe E-DCH and reference numerals 101 to 104 denote UEs using the E-DCH.As illustrated, the UEs 101 to 104 transmit data to the Node B 100 onE-DCHs 111 to 114.

The Node B 100 notifies the individual UEs 101 to 104 whether they arepermitted for E-DCH transmission or transmits to the UEs schedulinggrants indicating E-DCH data rates for them, based on information aboutbuffer occupancy and requested data rates or channel status informationreceived from the UEs. This operation is called scheduling of uplinkdata transmission. The scheduling is performed such that the noise riseor Rise over Thermal (ROT) measurement of the Node B does not exceed atarget ROT to increase total system performance by, for example,allocating low data rates to remote UEs (such as the UEs 103 and 104)and high data rates to nearby UEs (such as the UEs 101 and 102). The UEs101 to 104 determine their allowed maximum data rates for E-DCH databased on the scheduling grants and transmit the E-DCH data at thedetermined data rates.

Due to asynchronization between uplink signals from different UEs, theuplink signals interfere with one another. As the Node B receives moreuplink signals, an uplink signal from a particular UE suffers fromincreased interference, thereby decreasing reception performance in theNode B. This problem can be overcome by increasing the uplink transmitpower of the UE, but the increased transmit power in turn serves asinterference to other uplink signals. Thus, the reception performance isstill decreased in the Node B. The total power of uplink signals thatthe Node B can receive with reception performance at or above anacceptable level is limited. ROT represents uplink radio resources usedby the Node B, defined as

ROT=I _(o) /N _(o)  (1)

where I_(o) denotes power spectral density over a total reception band,that is, the total amount of uplink signals received in the Node B, andN_(o) denotes the thermal noise power spectral density of the Node B.Therefore, an allowed maximum ROT is total uplink radio resourcesavailable to the Node B.

The total ROT is expressed as the sum of inter-cell interference, voicetraffic and E-DCH traffic. With Node B-controlled scheduling,simultaneous transmission of packets from a plurality of UEs at highdata rates is prevented, maintaining the total ROT at or below a targetROT and thus ensuring reception performance all the time. When high datarates are allowed for particular UEs, they are not allowed for other UEsin the Node B-controlled scheduling. Consequently, the total ROT doesnot exceed the target ROT.

FIG. 2 is a diagram illustrating a typical signal flow for messagetransmission and reception on the E-DCH.

Referring to FIG. 2, a Node B and a UE establish an E-DCH in step 202.Step 202 involves message transmission on dedicated transport channels.The UE transmits scheduling information to the Node B in step 204. Thescheduling information may contain uplink channel status informationincluding the transmit power and power margin of the UE, and the amountof buffered data to be transmitted to the Node B.

In step 206, the Node B monitors scheduling information from a pluralityof UEs to schedule uplink data transmissions for the individual UEs. TheNode B decides to approve an uplink packet transmission from the UE andtransmits a scheduling grant to the UE in step 208. The scheduling grantindicates up/hold/down in an allowed maximum data rate, or an allowedmaximum data rate and an allowed transmission timing.

In step 210, the UE determines the TF of the E-DCH based on thescheduling grant. The UE then transmits TF information to the Node B,and uplink packet data on the E-DCH at the same time in steps 212 and214. The TF information includes a Transport Format Resource Indicator(TFRI) indicating resources required for E-DCH demodulation. The UEselects an MCS level according to an allowed maximum data rate set bythe Node B and its channel status, and transmits the E-DCH data in step214.

The Node B determines whether the TF information and the uplink packetdata have errors in step 216. In the presence of errors in either of theTF information and the uplink packet data, the Node B transmits a NACKsignal to the UE on an ACK/NACK channel, whereas in the absence oferrors in both, the Node B transmits an ACK signal to the UE on theACK/NACK channel in step 218. In the latter case, the packet datatransmission is completed and the UE transmits new packet data to theNode B on the E-DCH. On the other hand, in the former case, the UEretransmits the same packet data to the Node B on the E-DCH.

Under the above-described environment, if the Node B can receive fromthe UE scheduling information including, for example, information aboutthe buffer occupancy and power status of the UE, it allocates a low datarate to the UE if it is far from the Node B, is in a bad channel status,or has data of a lower service class. If the UE is near to the Node B,is in a good channel status, or has data of a higher service class, theNode B allocates a high data rate to the UE. Therefore, the total systemperformance is increased.

In the case where the Node B transmits a Relative Grant (RG) indicatingup/hold/down in the allowed maximum data rate of the UE as a schedulinggrant for the E-DCH, the signaling overhead of the RG reduces downlinkcapacity. Accordingly, a need exists for a method of reducing downlinksignaling overhead arising from transmitting a scheduling grant in NodeB-controlled scheduling.

SUMMARY OF THE INVENTION

An object of embodiments of the present invention is to substantiallysolve at least the above described problems and/or disadvantages and toprovide at least the advantages described below. Accordingly,embodiments of the present invention provide a method and apparatus forreducing downlink signaling overhead arising from transmitting ascheduling grant by which a Node B controls the uplink data rate of a UEin a situation where Node B-controlled scheduling and HARQ are used inan E-DCH-supporting mobile communication system.

Embodiments of the present invention also provide a method and apparatusfor effectively interpreting a scheduling grant that a Node B transmitsto control the uplink data rate of a UE in a situation where NodeB-controlled scheduling and HARQ are used in an E-DCH-supporting mobilecommunication system.

The above objects are substantially achieved by providing a method andapparatus for transmitting and receiving downlink control information ina mobile communication system supporting an uplink packet data service.

According to one aspect of the present invention, in a method oftransmitting packet data in an HARQ mobile communication system, asecond transceiver receives an RG as rate control information from afirst transceiver. The second transceiver sets the allowed maximum datarate of an HARQ process to which the RG is applied to the allowedmaximum data rate of an HARQ process previous to the HARQ process, ifthe RG indicates hold. The second transceiver transmits packet datawithin the set allowed maximum data rate to the first transceiver.

According to another aspect of the present invention, in a method oftransmitting control information for packet data reception in an HARQmobile communication system, a first transceiver determines an allowedmaximum data rate for a predetermined HARQ process for a secondtransceiver, and sets an RG as rate control information to hold if thedetermined allowed maximum data rate is equal to an allowed maximum datarate of an HARQ process previous to the predetermined HARQ process. Thefirst transceiver then transmits the RG to the second transceiver.

According to a further aspect of the present invention, in an apparatusfor transmitting packet data in an HARQ mobile communication system, aradio signal receiver despreads a signal received from a firsttransceiver with an allocated common channelization code. An RGsignaling interpreter detects an RG as rate control information from thedespread signal, and sets the allowed maximum data rate of an HARQprocess to which the RG is applied to the allowed maximum data rate ofan HARQ process previous to the HARQ process, if the RG indicates hold.

According to still another aspect of the present invention, in anapparatus for transmitting control information for packet data receptionin an HARQ mobile communication system, a Node B scheduler determines anallowed maximum data rate for a predetermined HARQ process for a secondtransceiver. An RG signaling generator sets an RG as rate controlinformation to hold if the determined allowed maximum data rate is equalto an allowed maximum data rate of an HARQ process previous to thepredetermined HARQ process. A radio signal transmitter transmits the RGto the second transceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of embodiments ofthe present invention will become more apparent from the followingdetailed description when taken in conjunction with the accompanyingdrawings in which:

FIG. 1 illustrates uplink packet transmission on the E-DCH in aconventional wireless communication system;

FIG. 2 is a diagram illustrating a conventional signal flow for messagetransmission and reception on the E-DCH;

FIG. 3 is a flowchart illustrating an operation for generating andinterpreting a scheduling grant according to an exemplary embodiment ofthe present invention;

FIG. 4 is a block diagram of a Node B transmitter according to anexemplary embodiment of the present invention;

FIG. 5 is a block diagram of a UE receiver according to an exemplaryembodiment of the present invention;

FIG. 6 is a flowchart illustrating an operation for generating andinterpreting a scheduling grant according to an exemplary embodiment ofthe present invention;

FIG. 7 is a flowchart illustrating an operation for generating andinterpreting a scheduling grant according to an exemplary embodiment ofthe present invention; and

FIG. 8 is a flowchart illustrating an operation for generating andinterpreting a scheduling grant according to an exemplary embodiment ofthe present invention.

Throughout the drawings, like reference numbers should be understood torefer to like elements, features and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the present invention will be described hereinbelow with reference to the accompanying drawings. In the followingdescription, detailed descriptions of well-known functions orconstructions are omitted for clarity and conciseness.

The following description of exemplary embodiments of the presentinvention is made in the context of the E-DCH in a UMTS system.

Node B-controlled scheduling is a technique of improving systemthroughput and coverage by efficient control of uplink ROT in a Node B.For this purpose, the Node B controls the E-DCH data rate of each UE. AnE-DCH data rate refers to the power ratio of a physical channel to whichthe E-DCH is mapped to a reference physical channel whose power iscontrolled. The E-DCH data rate is equivalent to an E-DCH TF or E-DCHtransmit power. That is, for a high E-DCH data rate, more power isallocated to the E-DCH.

The Node B-controlled scheduling can be considered in three ways. Oneway is to increase or decrease the allowed maximum data rate of a UE bya predetermined increment or decrement, or hold the allowed maximum datarate. The UE is able to transmit data in each TTI and the Node B signalsto the UE an RG indicating up/hold/down in the allowed maximum data rateinstead of an Absolute Grant (AG) indicating the absolute value of aspecific allowed maximum data rate. Typically, the RG is a 1-bitinformation that can be set to +1/0/−1 indicating up/hold/down. If theRG is 0, no signal is transmitted, that is, it indicates a DiscontinuousTransmission (DTX). The increment or decrement is predetermined and thusthe change of a data rate that the Node B can control for the UE at onetime instant is limited to the increment or decrement.

A second way is to signal an AG directly indicating the absolute valueof an allowed maximum data rate and a transmission timing for the UE.

A third way is to signal an RG and an AG in combination.

Considering that HARQ is applied to the E-DCH, the relationship betweenthe HARQ and the Node B-controlled scheduling will be described bow. Inan exemplary embodiment of the present invention, an N-channel SAW HARQscheme is taken. According to the N-channel SAW HARQ, a transmittertransmits different data in first through N^(th) TTIs and determineswhether to transmit new data or retransmit the transmitted data in(N+1)^(th) to 2N^(th) TTIs depending on ACK/NACK signals received forthe transmitted data. The exemplary embodiment of the present inventionis based on the assumption that the Node B signals an RG in the NodeB-controlled scheduling, the UE uses a 2 ms E-DCH TTI, and five HARQprocesses are defined. Thus, HARQ process numbers are repeated everyfive 2 ms TTIs in the order of 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, . . . . andso on. The value of an RG applies to the same process number. Forinstance, if the RG indicates “up” for HARQ process #2, the UE issupposed to increase an allowed maximum data rate applied to the latestHARQ process #2 by a predetermined level.

From the perspective of downlink signaling overhead, it may occur that aNode B scheduler transmits to a UE the same RG, for example, of +1 (up)successively for HARQ process #1 to HARQ process #5 according to the ROTof the cell and the channel status of the UE in an E-DCH system wherefive HARQ processes are defined for 2 ms TTIs. If the UE can find outthe RGs for HARQ processes #2 through #5 from the RG for HARQ process#1, the downlink signaling overhead of transmitting the RGs is reducedby a factor of five (one RG rather than five). In this context,exemplary embodiments of the present invention provide operations of theNode B and the UE to reduce signaling overhead for the case where thesame scheduling grant is repeated for a plurality of HARQ processes.

In accordance with an exemplary embodiment of the present invention, areference RG for a reference HARQ process (RG_reference) and anon-reference RG for a non-reference HARQ process (RG_non_reference) aregenerated separately to reduce downlink signaling overhead. Thereference HARQ process is notified by upper layer signaling or is fixed.

Given five HARQ processes, #1 through #5, HARQ process #1 is set as areference HARQ process and the other HARQ processes are set tonon-reference HARQ processes, for example. If the RG_non_reference isidentical to the RG_reference, the RG_non_reference is not signaled,thereby reducing the signaling overhead. For this purpose, the Node Band the UE make a distinction between the RG_reference and theRG_non_reference in generation and interpretation. To increase thereliability of transmission of the RG_reference, the RG_reference issent with higher power than the RG_non_reference.

Embodiment 1

FIG. 3 is a flowchart illustrating an operation for generating andinterpreting a scheduling grant according to an exemplary embodiment ofthe present invention.

Referring to FIG. 3, the Node B determines whether an HARQ process forwhich to allocate a data rate is a reference HARQ process in step 300.The HARQ process for which to allocate a data rate is an HARQ process tobe allocated to a current TTI and it is referred to as “a current HARQprocess”. If the current HARQ process is a reference HARQ process, theNode B sets an RG to +1 for a rate increase, 0 (that is, DTX) for norate change, or −1 for a rate decrease for the reference HARQ processaccording to scheduling in the Node B scheduler in step 302. Since theRG received from the Node B is intended for the reference HARQ process,the UE interprets an RG of +1 as a rate increase, an RG of 0 as no ratechange, and an RG of −1 as a rate decrease.

On the other hand, if the current HARQ process is a non-reference HARQprocess in step 300, the Node B determines whether an RG_referenceindicates up, hold or down in step 304. If the RG_reference indicatesup, the Node B sets an RG_non_reference for the current HARQ process to0 (that is, DTX) for a rate increase, −1 for no rate change, or +1 for arate decrease according to scheduling in the Node B scheduler in step306.

Since the RG received from the Node B is intended for the non-referenceHARQ process and the previously received RG_reference indicates up, theUE interprets an RG of +1 as a rate decrease, an RG of 0 as a rateincrease, and an RG of −1 as no rate change.

If the RG_reference indicates hold in step 304, the Node B sets theRG_non_reference for the current HARQ process to +1 for a rate increase,0 (that is, DTX) for no rate change, or −1 for a rate decrease accordingto scheduling in the Node B scheduler in step 308. Since the RG receivedfrom the Node B is intended for the non-reference HARQ process and theRG_reference indicates hold, the UE interprets an RG of +1 as a rateincrease, an RG of 0 as no rate change, and an RG of −1 as a ratedecrease.

If the RG_reference indicates down in step 304, the Node B sets theRG_non_reference for the current HARQ process to −1 for a rate increase,+1 for no rate change, or 0 (that is, DTX) for a rate decrease accordingto scheduling in the Node B scheduler in step 310. Since the RG receivedfrom the Node B is intended for the non-reference HARQ process and theRG_reference indicates down, the UE interprets an RG of +1 as no ratechange, an RG of 0 as a rate decrease, and an RG of −1 as a rateincrease.

In this manner, if the Node B intends to transmit an RG_non_referenceidentical to an RG_reference, it sets a DTX mode for a correspondingnon-reference HARQ process, thereby reducing signaling overhead.

The above-described operation will be described in great detail withreference to Table 1 and Table 2.

In Table 1 below, RG_reference values are mapped to ID_RG_referencevalues to have predetermined meanings. For an RG_reference of +1, theID_RG_reference is 2, indicating an increase in the allowed maximum datarate of a UE. For an RG_reference of 0, the ID_RG_reference is 1,indicating no change in the allowed maximum data rate. For anRG_reference of −1, the ID_RG_reference is 0, indicating a decrease inthe allowed maximum data rate. The Node B and the UE generate andinterpret RG_reference values according to Table 1.

TABLE 1 RG_reference ID_RG_reference Meaning +1 2 Up 0 1 Hold −1 0 Down

Generation and interpretation of an RG_non_reference can be expressed asthe following function of the RG_non_reference described in Table 2below.

TABLE 2 RG_non_reference ID_RG_non_reference +1 (ID_RG_non_reference+1)mod 3 0 ID_RG_non_reference mod 3 −1 (ID_RG_non_reference−1) mod 3

In Table 2, mod represents a modulo operation. “x mod y” equals theremainder of dividing x by y. As used herein, the modulo functionresults in an output ranging from 0 to |y−1| (a positive result). Forinstance, “1 mod 3=1” (three goes into one zero times, and leaves aremainder of one) and “−1 mod 3=2” (three goes into negative onenegative one times, and leaves a remainder of two). The Node B and theUE generate and interpret an RG_non_reference by calculating anID_RG_non_reference according to Table 2 and detecting anID_RG_reference having the same value as the calculatedID_RG_non_reference in Table 1.

For notational simplicity, five HARQ processes are defined, #1 through#5, and HARQ process #1 is set as a reference HARQ process.

In the case where the Node B signals an RG of +1 for the reference HARQprocess #1 to command an increase in the allowed maximum data rate ofthe UE (RG_reference=+1 and ID_RG_reference=2), if it then signals an RGof +1 for HARQ process #2 (RG_non_reference=+1), an ID_RG_non_referencefor HARQ process #2=(ID_RG_reference+1 mod 3=(2+1) mod 3=0. Therefore,looking an ID_RG_reference of 0 up to Table 1, the UE interprets theRG_non_reference as indicating a rate decrease. Thus, from the Node B'spoint of view, when commanding a rate decrease for HARQ process #2, theNode B signals an RG_non_reference set to 1.

If the Node B signals an RG of 0 for HARQ process #2(RG_non_reference=0), the ID_RG_non_reference=ID_RG_reference mod 3=2mod 3=2. Therefore, looking an ID_RG_reference of 2 up to Table 1, theUE interprets the RG_non_reference as indicating a rate increase. Thus,from the Node B's point of view, when commanding a rate increase forHARQ process #2, the Node B signals an RG_non_reference set to 0. If theNode B signals an RG of −1 for HARQ process #2 (RG_non_reference=−1),the ID_RG_non_reference=(ID_RG_reference−1) mod 3=(2−1) mod 3=1.Therefore, looking an ID_RG_reference of 1 up to Table 1, the UEinterprets the RG_non_reference as indicating no rate change. Thus, fromthe Node B's point of view, when commanding no rate change for HARQprocess #2, the Node B signals an RG_non_reference set to −1. In thisway, the Node B and the UE generate and interpret RGs (RG_non_referenceand RG_reference) until before the next reference HARQ process, that is,to HARQ process #5.

In the case where the Node B signals an RG of 0 (that is, DTX) for thereference HARQ process #1 to command no rate change in the allowedmaximum data rate of the UE (RG_reference=0 and ID_RG_reference=1), ifit then signals an RG of +1 for HARQ process #2 (RG_non_reference=+1),the ID_RG_non_reference for HARQ process #2=(ID_RG_reference+1 mod3=(1+1) mod 3=2. Therefore, looking an ID_RG_reference of 2 up to Table1, the UE interprets the RG_non_reference as indicating a rate increase.Thus, from the Node B's point of view, when commanding a rate increasefor HARQ process #2, the Node B signals an RG_non_reference set to +1.

If the Node B signals an RG of 0 for HARQ process #2(RG_non_reference=0, that is, DTX), theID_RG_non_reference=ID_RG_reference mod 3=1 mod 3=1. Therefore, lookingan ID_RG_reference of 1 up to Table 1, the UE interprets theRG_non_reference as indicating no rate change. Thus, from the Node B'spoint of view, when commanding no rate change for HARQ process #2, theNode B does not signal an RG in the DTX mode. If the Node B signals anRG of −1 for HARQ process #2 (RG_non_reference=−1), theID_RG_non_reference=(ID_RG_reference−1) mod 3=(1−1) mod 3=0. Therefore,looking an ID_RG_reference of 0 up to Table 1, the UE interprets theRG_non_reference as indicating a rate decrease. Thus, from the Node B'spoint of view, when commanding a rate decrease for HARQ process #2, theNode B signals an RG_non_reference set to −1. In this way, the Node Band the UE generate and interpret RGs (RG_non_reference andRG_reference) until before the next reference HARQ process, that is, toHARQ process #5.

In the case where the Node B signals an RG of −1 for the reference HARQprocess #1 to command a rate decrease in the allowed maximum data rateof the UE (RG_reference=−1 and ID_RG_reference=0), if it then signals anRG of +1 for HARQ process #2 (RG_non_reference=+1), theID_RG_non_reference for HARQ process #2=(ID_RG_reference+1 mod 3=(0+1)mod 3=1. Therefore, looking an ID_RG_reference of 1 up to Table 1, theUE interprets the RG_non_reference as indicating no rate change. Thus,from the Node B's point of view, when commanding no rate change for HARQprocess #2, the Node B signals an RG_non_reference set to +1.

If the Node B signals an RG of 0 for HARQ process #2(RG_non_reference=0, that is DTX), theID_RG_non_reference=ID_RG_reference mod 3=0 mod 3=0. Therefore, lookingan ID_RG_reference of 0 up to Table 1, the UE interprets theRG_non_reference as indicating a rate decrease. Thus, from the Node B'spoint of view, when commanding a rate decrease for HARQ process #2, theNode B does not signal an RG in the DTX mode. If the Node B signals anRG of −1 for HARQ process #2 (RG_non_reference=−1), theID_RG_non_reference=(ID_RG_reference−1) mod 3=(0−1) mod 3=2. Therefore,looking an ID_RG_reference of 2 up to Table 1, the UE interprets theRG_non_reference as indicating a rate increase. Thus, from the Node B'spoint of view, when commanding a rate increase for HARQ process #2, theNode B signals an RG_non_reference set to −1.

In this way, the Node B and the UE generate and interpret RGs untilbefore the next reference HARQ process, that is, until HARQ process #5.

Table 3 summarizes RGs (RG_reference and RG_non_reference) for HARQprocesses, set by the Node B.

TABLE 3 RG_non_reference When When When control RG_referenceRG_reference = 1 RG_reference = 0 RG_reference = −1 Up +1 0 +1 +1 Hold 0−1 0 −1 Down −1 +1 −1 0

FIG. 4 is a block diagram of a Node B transmitter according to anexemplary embodiment of the present invention.

For conciseness, channels other than a common code channel for carryingan RG (RG_reference or RG_non_reference) are not shown. The Node Btransmits k RGs to k UEs on one common code channel using a total of korthogonal sequences. The orthogonal sequences can be, for example,Hadamard sequences.

Referring to FIG. 4, the Node B transmitter is essentially divided intoan RG signaling generator 430 and a radio signal transmitter 450. The RGsignal generator 430 includes RG signaling mappers 402 to 416 throughrepeaters 414 to 428. The radio signal transmitter 450 includes a firstsummer 432 through a scrambler 446.

In operation, a Node B scheduler 400 generates an RG command(up/hold/down) for each UE taking into account the ROT of the cell and aresource allocation request from the UE. The RG signaling mappers 402 to416 map RG commands received from the Node B scheduler 400 to RG signalsaccording to the rule described as Table 3, taking into account HARQprocess numbers to which the RG commands are applied. Gain controllers406 to 420 adjust transmit power with appropriate RG gains 408 to 422,Gain_RG for the UEs, for reliable RG transmission. To increase thetransmission reliability of RG_reference, an RG gain for a referenceHARQ process can be set to be higher by a predetermined offset. In thiscase, the RG gain for the reference HARQ process is notified by upperlayer signaling or preset.

The power-controlled RGs are spread with orthogonal sequences 412 to 426allocated to the respective UEs to identify them in spreaders 410 to 424and repeated to a TTI length in repeaters 414 to 428. The repeated RGsfor all UEs are summed in the first summer 432 and converted to parallelsignals in a serial-to-parallel converter (SPC) 434. A channel spreader436 spreads the parallel signals with a common channelization codeC_(ch,sF,m) 438 allocated to the E-RGCH at a chip level. Among the chiplevel-spread signals, a Q-branch signal is phase-shifted by 90 degreesin a phase rotator 440 and then added to an I-branch signal in a secondsummer 442. A multiplexer (MUX) 444 multiplexes the sum signal withother channel signals and a scrambler 446 scrambles the multiplexedsignal, prior to transmission to the UEs.

FIG. 5 is a block diagram of a UE receiver according to an exemplaryembodiment of the present invention.

For conciseness, channels other than the common code channel forcarrying an RG are not shown. In the illustrated case of FIG. 5, areceiver in an arbitrary UE, UE #1 among k UEs mentioned with referenceto FIG. 4 is shown.

Referring to FIG. 5, the UE receiver is essentially divided into a radiosignal receiver 500 and an RG signaling interpreter 530. The radiosignal receiver 500 includes a descrambler 502 through a MUX 512, andthe RG signaling interpreter 530 includes an accumulator 514 through anRG signal decider 522.

In operation, a received signal is descrambled in the descrambler 502,channel-compensated in a channel compensator 504, and separated into anI-branch signal and a Q-branch signal in a Quadrature Phase Shift Keying(QPSK) demodulator 506. The I-branch and Q-branch signals are despreadwith a common channelization code C_(ch,sF,m) 510 allocated to theE-RGCH in a despreader 508, multiplexed in a MUX 512, and accumulated asmany times as repeated in the repeaters 414 to 428 in an accumulator514. The common channelization code C_(ch,SF,m) 510 is notified to theUE by a Radio Network Controller (RNC). The accumulated signal lasts theduration of one slot. A correlator 516 correlates the accumulated signalwith an orthogonal code 518, orthogonal code #1 allocated to the UE. AnRG signal extractor 520 compares the correlation with a predeterminedthreshold and outputs an RG signal set to one of +1, 0 and −1. The RGsignal decider 522 interprets the RG signal taking into account the RGsignal and the number of a current HARQ process number. Specifically,the RG signal decider 522 interprets the RG signal according to Table 1if a current HARQ process is a reference HARQ process, and according toTable 2 if the current HARQ process is a non-reference HARQ process.

While not shown, an E-DCH transmitter transmits uplink data within anallowed maximum data rate updated according to the interpreted RGsignal.

Embodiment 2

FIG. 6 is a flowchart illustrating an exemplary operation for generatingand interpreting a scheduling grant according to an embodiment of thepresent invention.

Typically, an up/hold/down command indicated by an RG applied to thesame HARQ process number. For instance, if the Node B signals an RGindicating up for HARQ process #2, the UE is supposed to increase anallowed maximum data rate applied to the latest HARQ process #2 by apredetermined level.

Referring to FIG. 6, the Node B determines whether a current HARQprocess to which a data rate is to be allocated is a reference HARQprocess in step 600. In the case of a reference HARQ process, the Node Bdetermines up/hold/down for the reference HARQ process with respect tothe allowed maximum data rate of the latest HARQ process in step 602. Onthe other hand, in the case of a non-reference HARQ process, the Node Bdetermines up/hold/down for the non-reference HARQ process with respectto the allowed maximum data rate of the reference HARQ process in step604. Since high reliability is required for RG_reference, RG_referenceis preferably transmitted at a higher transmit power level thanRG_non_reference. A transmit power adjustment value (Gain_RG) for thereference HARQ process is notified by upper signaling or preset.

In accordance with this embodiment of the present invention, a Node Btransmitter and a UE receiver are substantially identical to thoseillustrated in FIGS. 4 and 5 in terms of configuration and operation,except for RG generation and interpretation based on the above-describedrule illustrated in FIG. 6.

Embodiment 3

FIG. 7 is a flowchart illustrating an operation for generating andinterpreting a scheduling grant according to another exemplaryembodiment of the present invention.

Referring to FIG. 7, the Node B determines whether a current HARQprocess for which to allocate a data rate is a reference HARQ process instep 700. If the current HARQ process is a reference one, the Node Bdetermines an RG value of up/hold/down with respect to the latestallowed maximum data rate of the reference HARQ process for the UE instep 702. On the other hand, if the current HARQ process is anon-reference one in step 700, the Node B determines whether the latestRG of the reference HARQ process indicates up/hold/down in step 704.

If the RG_reference indicates up, the Node B compares the allowedmaximum data rate of the non-HARQ process with the latest allowedmaximum data rate of the reference HARQ process in step 706. For a rateincrease from the latest allowed maximum data rate of the reference HARQprocess, the Node B sets an RG_non_reference for the current HARQprocess to 0 that is, DTX), −1 for no rate change, or +1 for a ratedecrease. Since the RG received from the Node B is intended for thenon-reference HARQ process and the previously received RG_referenceindicates up, the UE interprets an RG of +1 as a rate decrease, an RG of0 as a rate increase, and an RG of −1 as no rate change.

If the RG_reference indicates hold in step 704, the Node B compares theallowed maximum data rate of the non-HARQ process with the latestallowed maximum data rate of the reference HARQ process in step 708. Fora rate increase from the latest allowed maximum data rate of thereference HARQ process, the Node B sets the RG_non_reference for thecurrent HARQ process to +1, 0 (that is, DTX) for no rate change, or −1for a rate decrease. Since the RG received from the Node B is intendedfor the non-reference HARQ process and the RG_reference indicates hold,the UE interprets an RG of +1 as a rate increase, an RG of 0 as no ratechange, and an RG of −1 as a rate decrease.

If the RG_reference indicates down in step 704, the Node B compares theallowed maximum data rate of the non-HARQ process with the latestallowed maximum data rate of the reference HARQ process in step 710. Fora rate increase from the latest allowed maximum data rate of thereference HARQ process, the Node B sets the RG_non_reference for thecurrent HARQ process to −1, +1 for no rate change, or 0 (that is, DTX)for a rate decrease. Since the RG received from the Node B is intendedfor the non-reference HARQ process and the RG_reference indicates down,the UE interprets an RG of +1 as no rate change, an RG of 0 as a ratedecrease, and an RG of −1 as a rate increase.

In this way, if the Node B intends to transmit an RG_non_referenceidentical to an RG_reference, it sets a DTX mode for a correspondingnon-reference HARQ process, thereby reducing signaling overhead.

Since high reliability is required for RG_reference, RG_reference ispreferably transmitted at a higher transmit power level thanRG_non_reference.

A transmit power adjustment value (Gain_RG) for the reference HARQprocess is notified by upper signaling or preset.

In accordance with the third embodiment of the present invention, a NodeB transmitter and a UE receiver are substantially identical to thoseillustrated in FIGS. 4 and 5 in terms of configuration and operation,except for RG generation and interpretation based on the above-describedrule illustrated in FIG. 7.

Embodiment 4

FIG. 8 is a flowchart illustrating an operation for generating andinterpreting a scheduling grant according to another exemplaryembodiment of the present invention.

Referring to FIG. 8, the Node B determines which one of commandsup/hold/down an RG for a current HARQ process will carry to the UE instep 800. If the RG indicates up or down, the Node B signals an RG of +1for a rate increase or an RG of −1 for a rate decrease in the allowedmaximum data rate of the UE in step 802 or step 804. This commandapplies with respect to the data rate of the UE used in the previousHARQ process of the same process number as that of the current HARQprocess.

An increment or decrement involved in the rate increase or decrease ispreset or notified by upper signaling, that is, Radio Resource Control(RRC) signaling from the RNC. Because the rate increase/nochange/increase in the allowed maximum data rate of the UE are performedwith respect to the data rate of the UE used in the previous HARQprocess of the same process number, the Node B scheduler can manage ROTresources efficiently.

If the RG indicates hold in step 800, the Node B signals an RG of 0,that is, in the DTX mode in step 806. The RG indicating hold applieswith respect to the allowed maximum data rate of the previous HARQprocess to the current HARQ process. Thus, in the case where the Node Bintends to allow the same allowed maximum data rate of the previous HARQprocess for the current HARQ process, the downlink signaling overhead isreduced. Also, even though the UE did not transmit data in the previousHARQ process at the allowed maximum data rate, the same allowed maximumdata rate can be ensured for the current HARQ process without any timedelay.

The above UE operation is generalized to

SG(k,n)=R_used(k,n−1)+delta  (2)

SG(k,n)=R_used(k,n−1)−delta  (3)

SG(k,n)=R_used(k,n−1,n)  (4)

SG(0,n)=SG(k−1,n−1)  (5)

The variables in Eq. (2) to Eq. (5) are defined as follows.

k: An HARQ process number. A total of k HARQ processes from HARQ process#0 to HARQ process #(k−1) are defined.

n: A TTI count for an HARQ process. n increases by 1 every K HARQprocesses.

SG(k, n): A serving grant indicating an allowed maximum data rate for aUE in an n^(th) TTI for a k^(th) HARQ process.

R_used(k, n): An actual data rate or power ratio of an E-DCH to areference channel used in the n^(th) TTI for the k^(th) HARQ process.

Delta: An increment or decrement in a rate increase or decrease based onan RG. It is preset or notified by upper signaling.

When the UE receives SG(k, n) for the n^(th) TTI of the k^(th) HARQprocess from the Node B, the allowed maximum data rate is determined inthe following way.

If RG(k, n)=+1, it indicates up. Thus, the allowed maximum data rate isincreased by delta from the data rate used in an (n−1)th TTI of thek^(th) HARQ process according to Eq. (2). If RG(k, n)=−1, it indicatesdown. Thus, the allowed maximum data rate is decreased by delta from thedata rate used in the (n−1)th TTI of the k^(th) HARQ process accordingto Eq. (3).

If RG(k, n)=0 (that is, DTX), it indicates hold. Thus, the allowedmaximum data rate depends on the HARQ process number k. If k is not 0,the allowed maximum data rate is the allowed maximum data rate of ann^(th) TTI of a (k−1)^(th) HARQ process according to Eq. (4). If k is 0,the allowed maximum data rate is the allowed maximum data rate of an(n−1)^(th) TTI of the (k−1)^(th) HARQ process according to Eq. (5).

In accordance with this embodiment of the present invention, a Node Btransmitter and a UE receiver are substantially identical to thoseillustrated in FIGS. 4 and 5 in terms of configuration and operation,except for RG generation and interpretation based on the above-describedrule illustrated in FIG. 8.

As described above, embodiments of the present invention advantageouslyincrease efficiency in generation of an RG as a scheduling grant bywhich to control the data rate of a UE in a Node and in RGinterpretation in the UE and reduces downlink signal overhead arisingfrom frequent RG transmissions for E-DCH transmission to which NodeB-controlled scheduling is applied.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

What is claimed is:
 1. A method of transmitting uplink packet data by aUser Equipment (UE) including a plurality of hybrid automatic repeatrequest (HARQ) processes in a mobile communication system, comprisingthe steps of: receiving a relative grant (RG) associated with a HARQprocess from a Node B by the UE; setting an allowed maximum power ratioof the HARQ process to the allowed maximum power ratio of an immediatelyprevious transmission time interval (TTI) of the HARQ process by the UE,if the RG indicates hold; and transmitting packet data within the setallowed maximum power ratio of the HARQ process to the Node B by the UE;wherein if the RG indicates hold, the reception step comprises the stepof receiving the RG from the Node B in a discontinuous transmission(DTX) mode by the UE.